1. Field of the Invention
The present invention relates to the papermaking arts. More specifically, the present invention is a method for manufacturing a papermaker""s press fabric wherein a top laminate layer is applied to a base fabric thereof in a spiral configuration and attached thereto with a heat-activated adhesive.
2. Description of the Prior Art
During the papermaking process, a fibrous web is formed by depositing a fibrous slurry, that is, an aqueous dispersion of cellulose fibers, on a moving forming fabric in the forming section of a paper machine. A large amount of water is drained from the slurry through the forming fabric during this process, leaving the fibrous web on the surface of the forming fabric.
The newly formed web proceeds from the forming section to a press section, which includes a series of press nips. The fibrous web passes through the press nips supported by a press fabric, or, as is often the case, between two press fabrics. In the press nips, the fibrous web is subjected to compressive forces which squeeze water therefrom, and which adhere the fibers in the web to one another to turn the fibrous web into a sheet. The water is accepted by the press fabric or fabrics and, ideally, does not return to the sheet.
The newly formed paper sheet finally proceeds to a dryer section, which includes at least one series of rotatable dryer drums or cylinders, which are internally heated by steam. The sheet is directed in a sinuous path sequentially around each in the series of drums by a dryer fabric, which holds the sheet closely against the surfaces of the drums. The heated drums reduce the water content of the sheet to a desirable level through evaporation, thereby completing the transformation of the fibrous web into a paper sheet.
It should be appreciated that the forming, press and dryer fabrics all take the form of endless loops on the paper machine and function in the manner of conveyors. It should further be appreciated that paper manufacture is a continuous process which proceeds at considerable speed. That is to say, the fibrous slurry is continuously deposited onto the forming fabric in the forming section, while a newly manufactured paper sheet is continuously wound onto rolls after it exits from the dryer section.
The press fabrics used in the press section are crucial components in the paper manufacturing process. One of their functions, as implied above, is to support and to carry the paper product being manufactured through the press nips.
The press fabrics also take part in the finishing of the surface of the paper sheet. That is, the press fabrics are designed to have smooth surfaces and uniformly resilient structures, so that, in the course of passing through the press nips, a smooth, mark-free surface is imparted to the paper.
Perhaps most importantly, the press fabrics accept the large quantities of water extracted from the wet paper in the press nip. In order to fill this particular function, there literally must be space (void volume) within the fabric for the water to go, and the fabric must have adequate permeability to water for its entire useful life. Finally, the press fabrics must be able to retain the water accepted from the wet paper upon exit from the press nip, so that the water will not rewet the paper.
Contemporary press fabrics are produced in a wide variety of styles designed to meet the requirements of the paper machines on which they are installed for the paper grades being manufactured. Generally, they comprise a woven base fabric into which has been needled a batt of fine, nonwoven fibrous material. The base fabrics may be woven from monofilament, plied monofilament, multifilament or plied multifilament yarns, and may be single-layered, multi-layered or laminated. The yarns are typically extruded from any one of the synthetic polymeric resins, such as polyamide and polyester resins, used for this purpose by those of ordinary skill in the paper machine clothing arts.
The woven base fabrics themselves take many different forms. For example, they may be woven endless, or flat woven and rendered into endless form with a woven seam. Alternatively, they may be produced by a process commonly known as modified endless weaving, wherein the widthwise edges of the base fabric are provided with seaming loops using the machine-direction (MD) yarns thereof. In this process, the MD yarns weave continuously back-and-forth between the widthwise edges of the fabric, at each edge turning back and forming a seaming loop. A base fabric produced in this fashion is placed into endless form during installation on a paper machine, and for this reason is referred to as an on-machine-seamable fabric. To place such a fabric into endless form, the two widthwise edges are brought together, the seaming loops at the two edges are interdigitated with one another, and a seaming pin or pintle is directed through the passage formed by the interdigitated seaming loops.
Further, the woven base fabrics may be laminated by placing one base fabric within the endless loop of another, and by needling a staple fiber batt through both base fabrics to join them to one another. One or both woven base fabrics may be of the on-machine-seamable type.
Moreover, a woven base fabric may be produced by spirally winding a woven fabric strip in accordance with the teachings of commonly assigned U.S. Pat. No. 5,360,656 to Rexfelt et al., the teachings of which are incorporated herein by reference.
Laminated base fabrics may also be produced by applying a top laminate layer to a woven base fabric of any of the above-noted types using the spiral manufacturing technique disclosed in U.S. Pat. No. 5,360,656. The top laminate layer may be a spirally wound flat-woven fabric strip; a strip of thermoplastic sheet material, such as, of polyurethane; or a strip of nonwoven mesh, such as that disclosed in commonly assigned U.S. Pat. No. 4,427,734 to Johnson, the teachings of which are also incorporated herein by reference. In each case, the width of the strip is much less than that of the woven base fabric, and several spiral turns thereof are required to completely cover the base fabric. Such top laminate strips have traditionally been prejoined to each other in a length and width required for a full-size press fabric. This full-width top laminate layer is then attached to the base fabric by needling a staple fiber batt into and through both layers to form a laminated base fabric. Ultimately, the batt is the main means for locking the top laminate layer to the base fabric.
The present invention is an improvement in the attachment of a top laminate layer to a base fabric, wherein the top laminate layer comprises at least one multi-component strip of material spiralled onto the base fabric, one of the components being a heat-activated adhesive.
Accordingly, the present invention is a method for manufacturing a press fabric for a paper machine wherein a top laminate layer is attached to a base fabric in a spiral manufacturing process using a heat-activated adhesive film.
More specifically, the present invention comprises the step of providing a base fabric for the press fabric. The base fabric may be of any of the standard varieties heretofore described, and is in the form of an endless loop having an inner surface, an outer surface, a first and second lateral edge, and a fabric width measured transversely between the lateral edges.
A multi-component strip for covering the outer surface of the base fabric in a closed helix is also provided. The multi-component strip has a beginning, a first lateral edge, a second lateral edge, and a strip width measured thereacross. The strip width is generally much less than the fabric width. The multi-component strip comprises at least a strip of top laminate layer material and a heat-activated adhesive film bonded to one side of the strip of top laminate layer material. The strip of top laminate layer material may be, for example, a woven fabric, a nonwoven mesh, or a sheet of thermoplastic material, such as of polyurethane.
The heat-activated adhesive film is used to attach the strip of top laminate layer material to the base fabric. To start the attachment process, the beginning of the multi-component strip is attached to the outer surface of the base fabric at a point on the first lateral edge thereof using heat and pressure. The side of the strip of top laminate layer material having the heat-activated adhesive film faces the base fabric during this process. The multi-component strip is oriented at a slight angle with respect to the first lateral edge, so that it may be spiralled onto the base fabric to completely cover it in a closed helix.
Continuing from the beginning of the multi-component strip, the side of the strip of top laminate layer material having the heat-activated adhesive film is attached to the outer surface of the base fabric in a closed helix having a plurality of turns using heat and pressure, wherein the first lateral edge of the turn of the multi-component strip being attached abuts against the second lateral edge of the turn of the multi-component strip previously attached to the outer surface, until the outer surface of the base fabric is completely covered by the strip in a closed helix. The multi-component strip is then cut at a point on the second lateral edge of the base fabric.
The present invention will now be described in more complete detail with frequent reference being made to the drawings identified hereinbelow.